Does anyone have any detailed information on British, German, or U.S. naval torpedo director telescopes? Specifically, I'm looking for information on telescopes made before 1919.

I'm building a presentation on Imperial Japanese Navy Torpedo Directors for the Nikon Historical Society convention this spring. I would like to determine if Nippon Kogaku copied British, German or U.S. telescopes in their early torpedo directors made in 1918/1919.

I own a British Torpedo Director Telescope Pattern 3341, dated 1917. It is manufactured by W. Ottway & Co of Ealing and bears serial number of either 17 or 148 (both are stated, and in the same place... it's not clear why).

It is 250mm long, and 35mm in diameter at its objective end.
It sports a simple crosshair and has moderate fixed zoom. I am not sure how I would measure this, however.

It can be focused and has a removable objective end cap that reduces its bore to a 6mm diameter (to limit glare in sun?)

It comes with its original wooden case, which is quite elegant.
Here are some photos, but I cannot resist putting one here that shows the view seen through it.

Curiously, this scope's aspect ratio (0.14) does not seem to match the scope shown in a handbook drawing of a scope mounted on a Patt 2391 Torpedo Director, whose aspect ratio appears to measure to 0.107:

Your British version is smaller than the four Japanese examples I have in my collection. My very early Japanese Topedo Director Telescope (circa 1915) is about 550mm long with a 40mm objective. The telescope is variable power (5-15), fixed focus with a cross-hair reticle. I thought the Japanese may have copied another naval design but perhaps this is not the case...

I don’t have photos online but I’ve published several articles on Japanese optics in previous issues of the “Nikon Journal”. Information on Japanese torpedo directors is very hard to come by. The WWII “U.S. Naval Technical mission to Japan” detailed some of their WWII directors but the report lacks good quality photographs. I can e-mail you a few photos for the telescopes in my collection if you are interested.